Method and apparatus for degassing liquids

ABSTRACT

An improved method and apparatus for degassing liquids which includes exposing a liquid containing entrained and dissolved gases to an improved degassing member. The degassing member is composed of a finely entwined porous material having physical properties causing the entrained and dissolved gases to coalesce near the surface of said member while allowing the degassed liquid to pass through said member.

This is a continuation of application Ser. No. 236,033, filed Mar. 20,1972, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates generally to an improved method andapparatus for removing entrained and dissolved gases from liquids andmore specifically to an improved method and apparatus for deaeratingsolutions used in connection with artificial kidney dialysis machinesand in connection with water purification systems such as reverseosmosis systems.

Although there are a variety of needs for solutions in which thedissolved gases have been removed, one of the primary uses for such asolution is in connection with artificial kidney dialysis machines. Afrequent problem encountered by many hospitals in the northern UnitedStates and Canada arose because of the presence of dissolved gases inthe cold water in these areas which was used in the preparation of thedialysate for use in artificial kidney units.

The dialysate is the physiological salt solution which passes throughthe dialyzer portion of the kidney unit and "rinses" wastes from theblood. The preparation of the dialysate includes heating the water tobody temperature after which the warm solution flows through thedialyzer where the turbulence releases the dissolved gases. Because thedialysate still contained many dissolved gases, it was necessary toinstall a bubble catcher in the blood line between the dialyzer and thepatient in order to trap air bubbles. However, such a bubble catcher hadto be evacuated every five to ten minutes throughout the ten to fourteenhour dialysis treatment to prevent air emboli from entering the patient.This was an extremely difficult and demanding task which if notaccomplished could be fatal to the patient. Consequently, there is anextreme need for an apparatus which would be able to efficiently andeconomically remove dissolved and entrained gases from solutions. In thepast, other attempts at removing dissolved gases from solutions haveincluded heating the solution and exposing the solution to ultrasonicenergy. None of these attempts, however, have been successfully appliedin the preparation of air free dialysate for use in kidney machines.

A second application for the present invention is in connection withwater purification systems such as reverse osmosis systems whichnormally remove over 90% of the dissolved salts in a solution but whichpasses most of the dissolved gases. Also, many technical and industrialprocesses require a gas free solution since dissolved gases caninterfere with mixing, upset flow and often impart unusual reactions.

SUMMARY OF THE INVENTION

In contrast to the prior art, the present invention does not utilizeheat, ultrasonic energy, or other means currently used to removedissolved gases from solutions. Rather, the present invention providesan improved apparatus and method for efficiently and economicallyremoving dissolved and entrained gases from solutions. With the presentinvention, the solution containing dissolved gases is introduced into adegassing chamber and exposed to a surface of a degassing membercomposed of a finely entwined and porous material which allows thesolution to pass through but which causes the dissolved air and gases tobe released from the solution in the form of thousands of tiny bubbleswhich coalesce on the surface of the degassing member. When thecollected gas bubbles become sufficiently large, they rise to the top ofthe degassing chamber and are discharged. When the present invention isused in the preparation of air free dialysate for use in connection withkidney dialysis units, patients can be dialyzed ten to fourteen hours ata time without fear of air bubbles entering the blood. Thus, in additionto increased efficiency and safety, numerous personnel hours are saved.

Accordingly, it is an object of the present invention to provide animproved method and apparatus for removing dissolved gases fromsolutions.

Another object of the present invention is to provide an improved methodand apparatus for removing dissolved gases from solutions without theuse of heat or ultrasonic energy.

Another object of the present invention is to provide an improved methodand apparatus designed to be used in connection with the preparation ofdialysate for use in artificial kidney machines for preventing theinjection of air bubbles into the blood stream of the patient.

Another object of the present invention is to provide an improved methodand apparatus for removing dissolved gases from solutions which utilizesa unique degassing member which allows the solution to pass through butwhich causes the dissolved and entrained gases to coalesce at thesurface of the member where they are collected and discharged.

A further object of the present invention is to provide an improvedmethod and apparatus for removing dissolved gases from solutions whichpermits artificial kidney patients to be dialyzed 10 to 14 hours at atime without fear of air bubbles entering the blood.

These and other objects of the present invention will become apparentwith reference to the drawings, the description of the preferredembodiment, and the appended claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view of the improved degasser of the presentinvention.

FIG. 2 is a cross sectional view of the improved degasser of the presentinvention taken along the line 2--2 of FIG. 1.

FIG. 3 is an expanded perspective view of the degassing member of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIGS. 1 and 2, the improved depassing apparatus 10 ofthe present invention includes generally a base 11, a casing 12 defininga degassing chamber 18 and a degassing member or cartridge 14 adapted toremove entrained and dissolved gases such as air, oxygen, nitrogen,carbon dioxide, etc. from a liquid.

More specifically, the base 11 includes an inlet port 15 connected witha degassing chamber 18 by an inlet conduit 16, and an outlet port 19connected with a second chamber 17 inside of the degassing member 14 byan outlet conduit 20. It should be noted that each of the ports 15 and19 contain internal threads 21 and 22 respectively enabling connectionsto be made between the ports 15 and 19 and auxiliary equipment in orderto supply liquid containing entrained and dissolved gases to thedegassing chamber 18 and to remove the deaerated liquid from the secondchamber 17. Although not specifically shown, it is contemplated that theliquid to be deaerated may be supplied to and the deaerated liquid maybe removed from the device 10 in a variety of ways such as positioning apump upstream of the inlet port 15, downstream of the outlet port 19, orpositioning a pump both upstream of the port 15 and downstream of theport 19 so that the liquid to be deaerated is caused to flow into thedegassing chamber 18, through the member 14, into the chamber 17, andout through the outlet port 19.

Integrally formed with the base 11 and extending upwardly therefrom is agenerally cylindrical center post 28 having a threaded portion 29 at itsupper end. As illustrated also in FIG. 3, the threaded portion 29extends through a cap member 30 and a gasket 31 and is adapted tothreadedly engage a nut 32 which may be tightened over the threadedportion 29 to secure the cap 30 against the upper edge of the member 14.Although the center post 28 is shown to be integrally formed with thebase 11, the center post 28 may be such that it is detachable from thebase 11 via a threaded connection. The base 11 and thus the center post28 may be constructed from a variety of materials such as polyethylene,polyvinyl chloride, stainless steel or aluminum, however, the inventorhas found that polyethylene is preferable in many instances where theincoming solution contains dissolved salts which would be likely tocorrode materials such as aluminum. It should be noted that the surfaces24, 25, 26 and 27 are all rounded surfaces to minimize the chance thatdissolved gases might collect in these areas to form an air bubble whichwould be released into the stream of the deaerated liquid.

Connected to the top surface of the base 11 is a cylindrically shapedhood or casing 12 which extends upwardly from the base 11 and around thedegassing member 14 to thereby define the degasing chamber 18 andenclose the member 14. The casing 12 includes a plurality of exteriorthreads 34 around its bottom edge which are designed to engagecorresponding internal threads in the base 11 to thereby secure thecasing 12 to the base 11. Like the base 11, the casing 12 may be made ofa variety of materials such as glass, stainless steel or polyethylenewhich in most cases is determined by the type of liquid being deaerated.Threadedly secured to the top portion of the casing 12 is a float valve35 which is designed to prevent the liquid introduced into the chamber18 from escaping and also, as will be discussed below, to allow air andother gases which are removed from the liquid to be discharged. Thefloat valve 35 includes a valve seat or gasket 36 which is supported bythe member 38 and a float ball 39 positioned below the seat 36 andadapted to seat against the seat 36 when the level of the liquid in thechamber 18 is sufficiently high. When the liquid level in the chamber isnot high enough to cause the ball 39 to seat against the seat 36, theball 39 is supported and retained by a stainless steel screen or floatrest 40. Each of the elements 36, 38, 39 and 40 are housed by the valvecasing 41 which is threadedly secured to the casing 12 by the threads42. The float ball 39 has a consistency and buoyance such that it willfloat on water. Thus, if the liquid in the chamber 18 reaches a level atwhich it would normally flow through the valve 35, the ball 39 is forcedupwardly against the seat 36 to prevent the water from escaping from thechamber 18. Although the preferred embodiment illustrates the casing 12as being secured to the base 11 by a threaded connection, it iscontemplated that the casing 12 may be clamped and sealed to the base 12by other mean.

Next, by referring generally to FIGS. 1 and 2 and more specifically toFIG. 3, the degassing member 14 is an annular shaped cartridge in whichthe bottom edge is adapted to seat in an annular groove 42 in the base11. It should be noted that the size of the groove 42 in the base 11must be machined to fit the particular type and size of member 14 to beused in the device 10 to prevent leakage of the solution from thechamber 18 into the chamber 17 between the groove 42 and the member 14.As described below, the bottom edge of the member 14 is urged into thegroove 42 by the cartridge securing means which includes the cap 30, thegasket 31, the center post 28, and the nut 32.

The cartridge cap 30 is a relatively circular member being constructedpreferably of stainless steel or polyethylene. The cap 30 includes ahole 44 through which the threaded end 29 passes and a beveled edge 45designed to engage the uppermost surface 43 of the member 14. By placingthe cartridge 14 in the groove 42 and positioning the cap 30 and thegasket 31 over the threaded end 29, the nut 32 can be tightened to forcethe beveled edge 45 of the cap 30 against the member 14 to preventliquid from passing between the cartridge 14 and the beveled edge 45.

When the member or cartridge 14 is secured in its operating position asshown in FIG. 1, the member 14 has its outer annular surface 45 exposedto the liquid in the degassing chamber 18, and its inner annular surface46, together with the bottom surface of the cap 30 defining a portion ofthe second chamber 17 into which the deaerated or degassed liquid flowsafter passing through the degassing member 14. Although the preferredembodiment illustrates the member 14 as having an annular shape, it iscontemplated that the size, shape and orientation of the member 14 maybe varied to suit the needs of the user. For example, if the user is notconcerned with the pressure drop across the member 14, a rectangularlyshaped member may function sufficiently well. The inventor hasillustrated an annular shaped member in the preferred embodiment becauseof the relatively large surface area which is exposed to the degassingchamber 18 and because this shape has worked well when used for thepreparation of deaerated dialysate for use with artificial kidneyequipment.

The material from which the degassing member 14 is constructed is adense, finely entwined, porous material having physical properties whichpermit liquid to pass through the material but which causes dissolvedand entrained gases in the liquid to coalesce near the surface of thematerial. As more and more gases coalesce on the surface of the member14, the collected gas bubble becomes sufficiently large so that the airbubble ascends to the top of the degassing chamber 18 due to thebuoyancy of the bubble. This air bubble is then released or dischargedthrough the valve 35. Although the member 14 may be constructed from avariety of different types of materials, the inventor has found that afinely entwined porous matrix constructed from materials such as porousceramic, epoxy and fiberglass resins, and filter spun materials worksufficiently well. More specifically, the inventor has found a CunoMicro-wynd filter having a desity of one micron and manufactured byAmerican Machine and Foundry Company and filter cartridges, Models AA,A, B and C, manufactured by W. and R. Balston Industrial Ltd. to besufficient for deaerating dialysate for use in artificial kidneymachines.

One of the physical properties which determines whether a certainmaterial will be sufficient for use as a degassing member 14 is thedensity. As mentioned above the inventor has found filter Models AA, A,B and C manufactured by W. and R. Balston Industrial Ltd. to havesufficient density for use in connection with the preparation of kidneydialysate. The density of these filters range from about 0.3 microns toabout 8.0 microns. Normally, in the field of the present invention,density refers to the size of particle which will not be allowed to passthrough the material. For example, a material having a density of 2microns will allow particles less than 2 microns to pass through thematerial but will filter out particles which are 2 microns in diameteror larger. The required density of a particular member 14 will dependupon the use of the deaerated liquid and upon the percentage ofdissolved gases desired to be removed. Generally, the lower the densityof the member 14, the lower the efficiency of removing entrained anddissolved gases from the liquid.

By referring to FIG. 1, the operation of the present invention may besummarized as follows: First, water or another liquid which is desiredto be degased is pumped through the inlet port 15 and conduit 16 intothe degasing chamber 18 where it is exposed to the outer annular surface45 of the degassing member 14. Immediately, the liquid will begin topass through the finely entwined porous material, however, the gasesdissolved in the liquid will coalesce at the surface 45 and will notpass through the member 14. Be cause of the restriction caused by themember 14, the liquid level in the chamber 18 will rise until the floatball 39 is forced against the seat 36, at which time the pressureforcing the liquid into the chamber 18 will tend to force the liquidthrough the member 14 into the chamber 17. During the passage of liquidthrough the member 14 into the chamber the dissolved gases will continueto coalesce on the surface 45 until a sufficiently large air bubble isformed, at which time the bubble of air will rise from the surface 45 ofthe member 14 to the top of the casing 12. When the collected gases atthe top of the casing 12 has amounted to a sufficient volume, the floatball 39 will drop and the collected gases will escape to the atmosphere.Simultaneously, the liquid level in the casing 12 will again rise sothat the collecting and releasing cycle will continue. The liquid whichpasses through the degassing member 14 into the second chamber 17 isdeaerated and may be discharged and put to any desired use.

Although the description of the preferred embodiment of the presentinvention has been very specific, it is contemplated that modificationsmay be made which would not depart from the spirit of the presentinvention. For example, the device of the present invention wouldoperate equally well if the entire system were inverted and the floatvalve 39 or a similar relieving valve was positioned within the base 11.Thus, it is intended that the scope of the present invention be dictatedby the appended claims rather than by the description of the preferredembodiment.

I claim:
 1. An improved degassing apparatus for use with artificialkidney machines for obtaining gas-free dialysis liquid for use in saidartificial kidney machines, said degassing apparatus comprising:housingmeans defining a hollow interior; a generally cylindrical degassingmember mounted in said housing and cooperating therewith to divide saidinterior into the outer and inner chambers, said degassing member havingouter and inner surfaces each defining a wall of said outer and innerchambers respectively; means for supplying a liquid containing entrainedand dissolved air to said outer chamber for exposure to the outersurface of said degassing member, and for passage through said degassingmember only into said inner chamber; said degassing member beingconstructed of finely entwined porous epoxy resin having physicalproperties and density sufficient to cause the entrained and dissolvedair in the liquid to coalesce near the outer surface of the degassingmember as the result of the passage of said liquid only through saiddegassing member; and vent means including a float valve in said housingmeans for discharge of air from said outer chamber, said float valvebeing disposed to prevent escape of liquid through said vent means; saidhousing defining a passageway for discharge of degassed liquid from saidinner chamber.
 2. The improved degassing apparatus of claim 1 whereinthe density of said degassing member is greater than 8.0 microns, butnot more than 0.3 microns.